Development of the balloon angioplasty technique began about fifteen years ago. The purpose of this technique is to open arteries in which the flow of blood has been impeded by build-up of arteriosclerotic plaques on the interior walls of the arteries. This technique consists of inserting a small diameter catheter into a blocked artery, the catheter having a small flexible balloon attached to its distal end. The catheter is moved through the artery until the balloon is placed in the area of the artery in which blood flow is impeded by plaque build-up. The balloon is then inflated in order to shear and disrupt the wall components of the vessel to obtain an enlarged lumen. With respect to arterial arthrosclerotic lesions, the relatively incompressible plaque remains unaltered, while the more elastic medial and adventitial layers of the vessel stretch around the plaque, thus opening the artery to permit improved blood flow. The balloon is then deflated and removed leaving plaque flattened against the artery walls.
After a period of several months, however, approximately one-third of the treated arteries sometimes undergo restenosis or a reclosing of the artery at the treated area, requiring repetition of balloon angioplasty. The restenosis problem has received considerable attention and several proposals have been made to deal with it.
The most promising approach to restenosis prevention has been the placement of a stent in a blood vessel which has undergone balloon angioplasty at the position in the vessel where the balloon was inflated. The stent is generally implanted inside a body vessel in a procedure immediately following the balloon angioplasty procedure. A stent (also referred to as a graft prosthesis, arterial endoprosthesis, intraluminal graft or intravascular mechanical support) is typically placed or implanted within the vascular system to reinforce collapsing, partially occluded, weakened or abnormally dilated localized sections of blood vessels or the like. Because stents generally have too large a diameter to fit through a pre-angioplasty, unexpanded, diseased portion of a vessel, conventional metal stenting procedures implant a stent or other intraluminal vascular graft subsequent to the initial balloon angioplasty procedure in which the vessel has been expanded. The simultaneous placement of a stent during the primary dilatation phase of a balloon angioplasty or other procedure would alleviate the restenosis problems and the need for a two-step procedure wherein the angioplasty procedure is performed first, followed by the stent placement procedure.
Another disadvantage of balloon angioplasty is the tendency of the balloon to adhere to the vessel wall during the dilatation phase of the angioplasty procedure. If a balloon adheres to a vessel wall, the procedure could produce dissection, or a splitting and tearing of the vessel wall layers, wherein the intima or internal surface of the vessel suffers fissuring. This dissection forms a "flap" of underlying tissue which may reduce the blood flow through the lumen, or block the lumen altogether. Typically, the distending intraluminal pressure within the vessel can hold the disrupted layer or flap in place. If the intimal flap created by the balloon dilation procedure is not maintained in place against the expanded intima, the intimal flap can fold down into the lumen and close off the lumen or become detached. When the intimal flap closes off the body passageway, immediate surgery is necessary to correct this problem. Thus, the adhesion of the balloon to the vessel wall can cause undesirable defects or irregularities in the wall surface, resulting in thrombosis, and restenotic episodes.
It would be advantageous to be able to provide a liner or a stent to cover and reinforce the interior portion of the vessel with a material that would provide a non-thrombogenic protective and supporting surface. Ideally, this protective liner would be provided during the primary dilatation phase of the angioplasty procedure rather than after the initial expansion of the vessel wall as in conventional angioplasty procedures. Thus, it would be extremely advantageous if the balloon itself, or a sleeve encasing the balloon, could be converted into a device capable of overcoming the two previously mentioned disadvantages: resentosis and adhesion.